The class of drugs exhibiting opium or morphine-like properties are referred to as opioids, or opioid agonists. As agonists, certain drugs are characterized as interacting with stereo specific and saturable binding sites in the brain and other body tissues and organs. Endogenous opioid-like peptides are present in areas of the central nervous system that are presumed to be related to the perception of pain; to movement, mood and behavior; and to the regulation of neuroendocrinological functions. Three classical opioid receptor types, mu (μ), delta (δ), and kappa (κ), have been studied extensively. Each of these receptors has a unique anatomical distribution in the brain, spinal cord, and the periphery. Most of the clinically used opioids are relatively selective for μ receptors, reflecting their similarity to morphine. However, opioid containing drugs that are relatively selective for a particular receptor subtype at standard therapeutic doses will often interact with multiple receptor subtypes when given at sufficiently high doses, leading to possible changes in their pharmacological effect. This is especially true as opioid doses are escalated to overcome tolerance.
The potential for the development of tolerance, physical and/or psychological dependence (i.e., addiction) with repeated opioid use is a characteristic feature of most drugs containing opioid analgesics. The possibility of developing addiction is one of the major concerns in the use of opioids for the management of pain. Another major concern associated with the use of opioids is the diversion of these drugs from a patient in legitimate pain to other individuals (non-patients) for recreational purposes.
Drug abusers and/or addicts typically may take a solid dosage form intended for oral administration containing one or more opioid analgesics and crush, shear, grind, chew, dissolve and/or heat, extract or otherwise tamper with or damage the dosage unit so that a significant portion or even the entire amount of the active drug becomes available for administration by 1) injection, 2) inhalation, and/or 3) oral consumption in amounts exceeding the typical therapeutic dose for such drugs.
There are three basic patterns of behavior leading to opioid abuse. The first involves individuals whose opioid drug use begins in the context of legitimate medical treatment and who obtain their initial drug supplies through prescriptions from appropriately licensed health care providers. Through an insidious process these individuals may ultimately begin seeking prescription drug supplies far exceeding their legitimate medical needs from multiple health care providers and/or pharmacies and/or from illicit sources diverted from otherwise legal drug distribution channels. The second pattern of abuse begins with experimental or “recreational” drug users seeking a “high” with no legitimate medical indication for drugs subject to abuse. A third pattern of abuse involves users who begin in one or another of the preceding ways and ultimately switch to orally administered drugs obtained from organized and legitimate addiction treatment programs.
There are various routes of administration an abuser may commonly employ to abuse an opioid containing drug formulation. The most common methods include 1) parenteral (e.g. intravenous injection), 2) intranasal (e.g., snorting), and 3) repeated oral ingestion of excessive quantities, for example, of orally administered tablets or capsules. One mode of abuse of oral solid drugs involves the extraction of the opioid component from the dosage form by first mixing the dosage form with a suitable solvent (e.g., water), and then subsequently extracting the opioid component from the mixture for use in a solution suitable for intravenous injection of the opioid to achieve a “high.”
Attempts have been made to diminish the abuse potential of orally administered drugs. These attempts generally centered on the inclusion in the oral dosage form of an antagonist which is not orally active but which will substantially block the effects of the drug if one attempts to dissolve the drug and administer it parenterally.
Despite all attempts, the misuse and abuse of pharmaceutical products continues to increase. Clearly there is a growing need for novel and effective methods and compositions to deter abuse of pharmaceutical products (e.g., orally administered pharmaceutical products) including but not limited to immediate release, sustained or extended release and delayed release formulations for drugs subject to abuse. In particular, such methods and compositions would be useful for opioid analgesics, for patients seeking drug therapy, which deter abuse and minimizes or reduces the potential for physical or psychological dependency.